esp32 syscalls.c: Use rom/uart.h for uart_tx_one_char prototype

components/esp32/syscalls.c

@@ -20,12 +20,11 @@
 #include <sys/reent.h>
 #include <stdlib.h>
 #include "rom/libc_stubs.h"
+#include "rom/uart.h"
 #include "freertos/FreeRTOS.h"
 #include "freertos/portmacro.h"
 #include "freertos/task.h"
 
-int uart_tx_one_char(uint8_t c);
-
 void abort() {
     do
     {